A paracorporeal left ventricular assist pump is proposed for clinical use by the Children's Hospital Cardiovascular Surgical Laboratory in conjunction with five participating hospitals in the Boston area: Massachusetts General Hospital, Peter Bent Brigham Hospital, Boston University Hospital, Beth Israel Hospital and West Roxbury Veterans Administration Hospital. A clinical patient selection protocol, approved by NHLBI in 1976, has been used during the past three years and will continue to be applied in case selection in the future. The blood pump is positioned on the right anterior chest wall, with inflow and outflow valved conduits which traverse the mediastinum. A pumping circuit is completed by inserting a curved metal inflow tube in the apex of the left ventricle and anatomosing an outflow Dacron conduit to the side of the ascending aorta. The power source consists of a pneumatic system which is synchronized with the electrocardiogram. The internal surfaces of the pump are covered with a layer of polyester fibrils which encourage deposition of a fibrin-cellular coagulum. No anticoagulation agents are employed until the time of tapering of pump flow, immediately prior to pump removal. Eight patients will be selected for LVAD implantation during each year of the proposed program. They will include those who cannot be adequately resuscitated at the end of a cardiac surgical operation, and others who develop cardiogenic shock within 72 hours following an uncomplicated cardiac surgical procedure.